Condensed Consolidated Statement of Shareholders' Equity (unaudited) - USD ($) $ in Millions	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income [Member]	Deferred Equity Compensation [Member]
Beginning balance at Dec. 31, 2016					$ 149
Increase (Decrease) in Shareholders' Equity
Net Income	$ 470
Other comprehensive loss	166
Less: reclassification adjustment for gains (losses) included in net income (loss), net of tax provision (benefit) of $0 and $(1)	0
Ending balance at Jun. 30, 2017					315
Beginning balance at Mar. 31, 2017					206
Increase (Decrease) in Shareholders' Equity
Net Income	153
Other comprehensive loss	109
Less: reclassification adjustment for gains (losses) included in net income (loss), net of tax provision (benefit) of $0 and $(1)	0
Ending balance at Jun. 30, 2017					315
Increase (Decrease) in Shareholders' Equity
New accounting pronouncement or change in accounting principle, effect of change on net income					32
New accounting pronouncement or change in accounting principle, effect of change on net income | Accounting Standards Update 2016-01 [Member]					(32)
Beginning balance (in shares) at Dec. 31, 2017		116,020,852
Beginning balance at Dec. 31, 2017	6,839	$ 1	$ 573	$ 5,892	372	$ 1
Increase (Decrease) in Shareholders' Equity
Net Income	272			272
Dividends ($0.32 per share)	(37)			(37)
Common stock repurchases (in shares)		(6,951,126)
Common stock repurchases	(250)	$ 0	(250)
Share-based compensation and other (in shares)		544,488
Share-based compensation and other	(2)	$ 0	(2)
Other comprehensive loss	(188)				(188)
Less: reclassification adjustment for gains (losses) included in net income (loss), net of tax provision (benefit) of $0 and $(1)	(3)
Ending balance (in shares) at Jun. 30, 2018		109,614,214
Ending balance at Jun. 30, 2018	6,634	$ 1	321	6,159	152	1
Beginning balance at Mar. 31, 2018					214
Increase (Decrease) in Shareholders' Equity
Net Income	75
Other comprehensive loss	(62)
Less: reclassification adjustment for gains (losses) included in net income (loss), net of tax provision (benefit) of $0 and $(1)	(1)
Ending balance (in shares) at Jun. 30, 2018		109,614,214
Ending balance at Jun. 30, 2018	$ 6,634	$ 1	$ 321	$ 6,159	$ 152	$ 1